Recurrent perivascular inflammation induced by lipopolysaccharide (endotoxin) results in the formation of atheromatous lesions in vivo

Bacteria and viruses are suspected to induce arteriosclerosis; however, most investigators have focused on coincidences rather than causal relationships. The aim of this work was to establish a rabbit model in which the vessel reaction to local perivascular injection of defined bacterial products can be analyzed. A total of 23 rabbits were randomized to four groups. Groups A and B were fed a normal diet, groups C and D were fed a cholesterol-enriched diet. Groups A and C were treated with a single perivascular injection of bacterial lipopolysaccharide (LIPS, endotoxin) placed next to auricular, carotid and femoral arteries, and sodium chloride placed next to the contralateral arteries (control). Group B and D animals were treated with repeated perivascular injections over 90 days. Vascular tissues (n = 116 treated segments of 23 rabbits) were analyzed using morphometry at histology, and using immunohistochemistry to detect macrophages, lymphocytes and vascular smooth muscle cells. LIPS treatment resulted in transient focal intima thickening. After single LIPS application, no increase in atheromatous lesion formation was observed in comparison with controls (group C, lesion area index 0.031 +/- 0.012 vs 0.015+/- 0.006, P = 1.0). Repeated LIPS application resulted in significant atheromatous lesion formation compared with saline control (group D, lesion area index 0.148+/-0.049 vs 0.008 +/- 0.006, P= 0.003) in hypercholesterolemic rabbits. Repeated LPS inflammation in normocholesterolemic did not lead to atheromatous lesion formation (intima media ratio 0.04+/-0.01 vs 0.04+/-0.007, P = 1.0). Single perivascular administration of low-dose bacterial LIPS resulted in transient focal intimal thickening, while significant increase in lesion formation occurred after repeated LIPS application in cholesterol-fed animals. In conclusion, this animal model will allow the assessment of the impact of defined dosages of different bacterial pathogens onto the vascular wall in the context of atherogenesis. The atheromatous lesion-promoting effect of repeated perivascular administration of LIPS supports the hypothesis that bacterial pathogens may be involved in atherogenesis.